Titanium alloy articles resistant to hydrogen absorption for dynamoelectric machines



H. B. BoMBl-:RGER ETAL 3,113,227 TITANIUM ALLOY ARTICLES RESISTANT T0 HYDROGEN ABSORPTION FOR DYNAMOELECTRIC MACHINES Flled March 21, 1960 v IN V EN TRS. Ha WA @D 5f BOMBEPGEA?. BY EPNEsrE KVA P5K.

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United States Patent O 3 113,227 TITANIUM ALLGY RTECLES RESISTANT T0 HYDROGEN ABSRPTIN FR DYNAMO- ELECTRIC MACES Howard B. Bamberger, East Liverpool, Ohio, and Ernest E. Knapek, Beaver, lPa., assignors to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey Filed Mar. 21, 1960', Ser. No. 16,405 S Claims. (Cl. S- 55) This invention pertains to articles made of titanium base alloys which are highly resistant to hydrogen absorption at temperatures up to about 400 C., and means for minimizing hydrogen absorption in articles made of titanium and titanium base alloys which are exposed in service to hydrogen or hydrogen-containing atmospheres at such elevated temperatures. n

The invention finds special application in large electrical generators of the hydrogen cooled type, for constructing certain components of which such as the armature retainer and end rings and the like, there is a demand for a strong, ductile and non-magnetic material ot' high strength-to-weight ratio, which at the same time is resistant to absorption of the hydrogen atmosphere employed for cooling and which is not embrittled thereby over long periods of use.

The present invention provides in one of its aspects certain titanium base alloys which inherently meet the aforesaid requirements to a high degree, and which when made into articles such as armature retaining rings, end rings and the like, and appropriately surface treated, are highly resistant to hydrogen absorption at operating temperatures including overload conditions of such generators.

The invention provides in another of its aspects a modilied type of hydrogen atmosphere containing a small fraction of oxygen and/ or water vapor, for use in such generators for cooling purposes, and adapted substantially to inhibit appreciable hydrogen absorption by components thereof exposed to such atmosphere and made of titanium or titanium base alloys.

3,ll3,227 Patented Dec. 3, l963 Frice are given a surface treatment, as by vacuum annealing and exposure to air prior to placing in service, their resistance to hydrogen absorption at elevated temperatures is greatly enhanced.

We have further discovered that if the hydrogen atmosphere to which such articles are exposed in service contains a small amount of oxygen and/or water vapor, in the range of about 0.1 to 1% by volume of oxygen and/ or Water vapor, preferably the former, that articles made of titanium and titanium base alloys, particularly those of the alpha or predominantly alpha type aforesaid, are rendered substantially immune to hydrogen absorption as a result of such exposure.

Our researches in the experimental hydrogenation of titanium alloys at temperatures up to 700-800" C., have clearly demonstrated that the rate of hydrogen absorption is a function of the alloys crystallographic form and that it is markedly influenced by the purity of the hydrogen employed. We have found that the alpha, titanium base alloys are considerably more ditiicult to hydrogenate than those of the beta or alpha-beta types, and that for etectively hydrogenating the former, pure, dry hydrogen is required.

Large alternating current electrical generators, of the hydrogen atmosphere cooled type, are designed to operate normally below 200 C., but overloads can raise the temperature for short periods as high as 300 C., While arcing can result in brief, localized temperature excursions up to about 400 C. Therefore, if the inherent advantages of titanium base alloys as regards high strength-toweight ratio and non-magnetic properties are to be successfully utilized for components as aforesaid in such generators, alloys of this type must be provided which are inherently resistant to hydrogen absorption or may be rendered so by suitable surface treatment, and/or which are employed under conditions such that absorption will not occur over prolonged periods of operation.

The present invention provides these features as will now be shown by reference to the test data given in Tables Il-V below made on titanium and titanium base alloys of the compositions given in the following Table I:

TABLE I hemcal Analyses of Titanium Alloys Tested Composition Percent-Balance Titanium l Nominal.

The invention is based in part on our discovery that titanium base alloys of an all-alpha or predominantly alpha type, and preferably containing about 5 to 30% of one or more of the alpha promoters aluminum, tin and zirconium, but not to exceed about 23% tin, or 10% aluminum, and such as may also contain up to about 5% of one or more of the isomorphous beta promoters vanadium, columbium, molybdenum and tantalum, are not embrittled on prolonged exposure to hydrogen atmospheres at elevated temperatures up to about 400 C., and are moreover far more resistant to hydrogen absorption under such conditions than are the titanium base alloys of the mixed alpha-beta or all-beta typesV We have further discovered that when articles made of these alloys In the alloys of the above table, that designated A70 is commercial purity titanium containing only small amounts of contaminants, such as carbon, nitrogen and iron, as shown, and also a small amount of oxygen although no analysis was made for the oxygen content. The alloys AllOAT and RC900 are of the all-alpha type while that designated Cl20AV is of the substantially allalpha type owing to the relatively high alpha-solubility of the beta promoter vanadium. Alloy 8-1-1 is likewise of the substantially all-alpha type owing to the small contents of the beta promoters vanadium and molybdenum and the alpha-solubilities thereof. Alloy CAMO is of the mixed alpha-beta type, While BlZOVCA and 12-4 are substantially all-beta alloys.

For purposes of `conducting the tests set forth in Tables H-V presented and discussed below, the alloys shown in 4 TABLE Il-Continued Table il were prepared by forging and rolling into strip Hoy surface Condition Test H Analy-u and thereupon vacuum annealing for 4 hours at 1400 F. Atmosphore SCS1 imp-111.u followed by rapid furnace cooling in the cold zone of the 5 furnace. Standard nicrotensile specimens and stress R090() as vgguulflffflled---f gotlxposedh" l samples were prepared, degreased, and placed in Pyrex 5 vials 9.5 long by 0.5 in diameter. The vials were then a (53 evacuated and given the atmospheres listed in Tables II-V, vacuum annealed 5nd 2 only 5 21111 inc., as discussed below. The hydrogen arld argOIlngaSeS vacumcgnnealed and 11201115, used in these experiments were dried with Drierite. Afair oxidized. ter the tubes were flame sealed, they were placed 1n capped @13a-,AMLO as Vacuum annealednm steel pipes (for safety) and exposed at the temperatures gg and times indicated in Tables II-V. Hydrogen determina- D0: tions were made both before and after exposures. vamug--h-caled and- The following Table II gives the hydrogen aosoi'piioii am) -Ze in 30 days at 200 C. of a series of specimens prepared as vaiirdiazirdiealed and above and exposed to atmospheres comprising, lrespectively, dry hydrogen and dry hydrogen to which variable C120AV as vacuum annealed amounts of oxygen, nitrogen and water, by volume, had 4 been added as indicated in the table, the comparison in each instance being made with reference to the hydrogen 8 content of a non-exposed specimen as shown in the table. VaQuum-d-amealed and 7 alf 0X1 lZC( TABLE H B12OVCA as vz1i)euumarinealed got clxposed) Hydrogen Absorption in 30 Days at 200 C. 0' 2 on y 12-4 Do... (not exposed) 10 Do Hg only 12 Alloy Surface Condition Test H Analy- Atrnospliere 1 ses, p.p.m.2

1 Note that first analysis of each alloy gives the base hydrogen level. 2 Room temperature pressure of one atmosphere. Note that controls A as velijouum annenled giet e1xp0Sed) 7J were not exposed. Additions were in percent by volume.

0 3 o 1 d d s7g The data of Table II establishes that the hydrogen abarflilzefmca c an V sorption 'for each of these alloys was substantially nil at vnouuindanrilcaled and 8 30 temperatures up to 200 C., whether exposed to pure, dry a 0X1 e hydrogen or to that containing additions of oxygen, nitro- AllOA'I as vigcuurn annealed 'g gen 01' water Vapor,

o G This same high resistance to hydrogen absorption was H 6 H2O 40 also noted on specimens similarly processed and exposed Hi only/fo 5 at 200 C. for periods of 6 to 12 months, as shown in the follow-ing Table IH which also includes the room temvacuurn annealed and Hg only 7 air oxidized. perature tensile properties of the specimens following ex-` See footnotes at end of table. Posuref TABLE III Mechanical Properties and Hydrogen Absorption After 6 and l2 Months at 200 C.

Ult. 0.2% Percent H Analyses, p.p.rri.l Tens. Offset Elong RA, Time, Alloy Str., Yield in 12 percent mos. Atmosphere 2 KSI Str., Non- Stressed KSI stressed 130000 114.5 104.0 13.3 43.2 24 23 5 H4 only.

112.4 105,2 15.0 39.2 17 17 5 Hi|1%1-I2O. 117.9 109.4 20.0 47.5 17 25 5 Argon only. 119.5 112.4 13.3 41.0 24 54 12 H2 only. 120.0 112.7 13.3 45.0 22 25 12 H2+1% H10. 120.0 112.5 18,3 46.2 27 12 Argon only.

3-1-1 144.3 122,5 15.0 33.3 27 45 5 H2 only.

145.0 120.3 13.3 43.3 15 40 5 E24-14751120. 138.4 115.6 16.7 39.2 21 21 6 Argon only. 152.5 123.3 15.0 40. 5 37 33 12 H2 only. 152.2 127.4 13.3 34.4 32 53 12 11H-17.31110. 147.5 127,5 16.7 37.5 30 29 12 Argon only.

CAV 135.3 122.2 13.3 35.1 30 50 5 H2 only.

135.2 121.1 15.7 39.1 41 33 5 H1+1%H1O. 135.5 1 .5 15.0 41.2 14 23 5 Argon only. 142. 5 130.1 15.0 41.2 35 35 12 Hi only. 135.5 124.0 13.3 42.0 20 30 12 H1+1%Hi0. 141.4 127.6 15.0 48.6 17 33 12 Argon only.

CAl\ro 152.1 149.4 15.0 45.3 20 51 5 H2 only.

140.5 137.7 15.7 51.3 13 39 5 1125-1211120. 150.9 143.2 15.0 47.4 22 21 5 Argon only. 153.5 152.2 15.7 42.9 29 53 12 H2 only. 151.3 150.7 13.3 55.1 10 47 12 E24-1% H20. 153.9 152.0 3.3 54.4 30 29 12 Argon only.

1 Specimens exposed to argon serve as controls. 2 Room temperature pressures of one atmosphere. Water additions in percent by volume.

From Table III it Will be seen, however, there is considerable hydrogen pickup in the stressed portions of the samples tested when exposed to pure, dry hydrogen, but that the absorption is greatly reduced or completely eliminated if the hydrogen atmosphere contains a small amount of moisture such as about 1% yby volume of water vapor. It will be further noted from Table III that Where hydrogen absorption does occur, the alloys are not embrittled thereby, the tensile elongations and area reductions being excellent following the tests.

The following Table IV shows the elect on mechanical properties and hydrogen absorption of exposing specimens for 30 days fat 400 C. under the various testing conditions indicated, namely, exposure to dry hydrogen, also to hydrogen containing 1% by volume of oxygen, `also to hydrogen containing 1% by volume of nitrogen, also to hydrogen containing 0.1% by volume of water, all for the surface condition of the alloy specimens as Vacuum annealed, and in addition for the surface condition of a specimen of each alloy `as vacuum :annealed and air oxidized and then exposed to dry hydrogen only.

TAB LE IV as applied particularly to the lalpha alloys, with respect to which the oxygen addition was in some instances more effective than that of the water vapor and v-ice versa. I n the case of the alpha-'beta alloy C135AMO, however, the oxygen addition was not nearly so effective as the water vapor addition to the hydrogen atmosphere, the saine being ytrue to a lesser degree for the C120AV alloy, which although of the alphaJbeta type has predominantly the alpha `structure at room temperature. Also, still referring to Table IV, it will be noted that Where the hydrogen pickup was excessive, i.e., that resulting from exposure of the specimen to dry hydrogen only, there was no embrittlement of the alloy, the tensile elongations and area re- Mechanz'cal Properties and Hydrogen Absorption in Days at 400 C.

0.2% Oset Percent Alloy Ult. Tens. Yield Elong. RA, H Analyses Atmosphere 2 Str., KSI Str., KSI in 1/2" percent ppm. (l)

A76 92. 6 65.4 33. 3 47.3 7 (not exposed).

95. 6 66. 7 28. 3 43. 4 608 H2 only. 91. 2 66. 2 33. 3 47. 5 21 HTI-1% O2 94. 9 n 89. 6 31. 7 43. 2 531 Hai-1% N2. 92. 2 65. 7 31. 7 36. 7 9 HTI-.1% H2O 93. 4 66.7 28. 3 48. 2 3 86 H2 only.

A116AT 128.2 113. 9 20. 0 46. 7 4 (not exposed).

130. 1 116. 3 31. 7 38. 4 Do. 158. 6 151. 6 13. 3 29. 6 1,020 Hz only. 133.6 129. 3 20.0 40. 5 61 HV1-1% Oz. 128. 7 118.0 23. 3 44.3 (4) HTI-1% N2. 130. 7k 122.5 23. 3 34. 7 46 H2l.1% H2O 132. 6 122. 5 23. 3 42.9 3 69 H2 only.

R090() 112.3 96.4 23.3 40. 5 4 (not exposed).

113. 3 102.8 20.0 35. 7 4 Do. 116. 2 10B. 4 21.7 35. 5 (4) H2 only. 115.8 110. 8 23.3 32. Q 14 Erl-1% Oz. 135. 7 128.0 16.7 31.4 364 11H-1% N2. 117. 6 112. 8 20.0 38.0 20 HTI-.1% H2 118. 5 111. 1 21. 7 42. 3 3 25 H2 only.

C135AMO- 151. 3 143. 9 15. 0 33. 4 8 (not exposed).

152. 2 146.8 16. 7 41. 7 6 Do. 167. 7 152. 7 16. 7 33. 7 905 Hz only. 162. 3 152.1 15.0 31. 4 110 HTI-1% O2. 168. 6 115. 4 15.0 35. 7 283 HV1-1% Ni. 143. 5 129. 3 18. 3 43. 2 10 11H-.1% H2O. 156. 4 142. 9 16. 7 40. 2 3 107 Hz only.

C120AV 127. 6 105. 8 20.0 38. 7 4 (not exposed).

125.0 94. 4 16. 7 37. 0 4 D0. 150. 5 140. l 18. 3 34. 4 645 Hz only. 143.0 130. 3 18.3 40. 9 94 HTI-1% O2. 138. 5 113. 3 16. 7 89. 7 (4) Erl-1% N2. 140.3 124. 2 18.3 38. 1 46 HV1-.1% H2 136. 0 105. 6 18. 3 46. 6 3 40 Hz only.

13120VCA 132. 2 116. 6 26. 7 47. 6 12 (not exposed) 131.0 111. 8 28. 3 44. 4 12 D0. 107. 6 1, 135 H2 only.

12-4 141. 5 129. 2 13. 3 29. 1 10 (not exposed).

145. 5 136. 4 11. 7 42. 5 10 D0. 179. 1 165. 9 3. 3 19. 3 675 H2 only.

1 Note that first analysis oi each alloy gives the base level. 2 Room temperature pressure of one atmosphere.

Note that controls were not exposed.

3 Surface condition of specimens as vacuum annealed except those marked (3) Wh ich were vacuum annealed and air oxidized.

4 Vial ruptured during test.

Referring to the data in Table IV, it will be seen that the ductions being` excellent after the exposure. As further alpha alloys are inherently less susceptible to hydrogen absorption than are the alloys of the alpha-beta or allbeta types as seen by comparison of the results for the alpha materials A70, AllOAT, RC900- and C120AV as compared to the results for the alpha-beta alloy C135AMO and the beta alloys B120VCA and 12-4. It will further be noted that the surface treatment consisting in vacuum annealing and thereupon air oxidizing the specimens tremendously reduced the absorption on exposure to dry hyshown, some strengthening of the alloy resulted from the hydrogen pickup. And finally it is to be noted from the dat-a of Table IV, that nitrogen additions to the hydrogen were quite ineffective in reducing hydrogen pickup.

The following Table V gives comparative test results on certain of the alloys of Table I, processed as aforesaid, as regards effect on mechanical properties and hydrogen absorption following exposures `at 400` C. for 30 and 90 days, respectively, in both the stressed and unstressed condrogen, particularly lso with respect to the alpha alloys. ditions of the specimens.

TABLE v Mechanical Properties and Hydrogen Absorption After 30 and 90 Days at 400 C.

Ult. 0.2% Percent H Analyses, p.p.m.1 Tens. Offset Elong. RA, Time, Alloy Str., Yield in Percent days Atmosphere 2 KSI Str., Non Stressed KSI stressed H0900 134. 4 128. 7 16. 7 43. 0 147 280 30 11H-.1% H20.

120.3 114. 5 15.0 40.6 35 57 30 11H-1% Oz. 116. 9 112. 3 15. 0 35. 6 18 37 30 Argon only. 136.9 130. 4 15. 0 31.0 248 945 90 Hz-F.1% H2O. 121.1 114.2 18.3 43.7 7 47 90 Eri-1% O2. 119. 3 113. 2 15. 0 33. 7 6 90 Argon only.

8-1-1 146. 2 122. 9 15. 0 43.0 143 310 30 HTI-.1% H2O.

153. 3 126.1 6. 7 20. 4 100 102 30 HTI-1% Oz. 150. 3 124. 5 13. 3 30. 5 38 38 30 Argon only. 127.8 110. 8 10.0 40. 9 356 Sl 90 11H-.1% H2O. 163. 2 140. 1 11. 7 27. 7 271 324 90 :HH-1% O2. 151. 7 125. 4 13.3 29.1 8 16 90 Argon only.

C120AV 139.5 127. 6 13.3 42. 5 84 160 30 HTI-.1% H2O.

142. 7 130.1 15. 0 45.1 85 60 30 11H-1% O2. 140. 3 125.0 16. 7 25. 3 25 37 30 Argon only. 144. 3 134. 6 16. 7 42. 8 238 456 90 Hq--.lZJI-IZO 148.0 135. 4 15. 0 40. 3 226 192 90 11H-1% 02. 142. 7 129. 7 15. 0 43. 5 3 51 90 Argon only.

C135AMO 156. 4 151.2 13.3 42.0 1.15 349 30 HV1-.1% H2O.

158. 0 151.9 15.0 40. 2 214 25S 30 Erl-1% O2. 152. 4 146.3 13.3 38. 7 22 29 30 Argon only. 158. 3 151.6 15. 0 41. 8 164 1, 240 90 H2:l:.1% H2O. 161. 6 16. 7 44. 7 362 326 90 11H-1% O2. 153. 4 149. 4 13.3 40. 7 10 86 90 Argon only.

1 Specimens exposed to argon serve as controls. 2 Room temperature pressures of one atmosphere.

Referring to the data in Table V, it will be seen that the water vapor addition to the hydrogen atmosphere was in general not nearly so effective as the oxygen addition in suppressing hydrogen absorption in the specimens. Also that whereas the hydrogen absorption for the oxygen addition, was in general quite small for exposures up to 30 days, that in general there was a substantial increase in pickup when the exposure was continued to 90 days. But again the Table V tests demonstrate `the superiority of the alpha alloys as regards resistance to hydrogen absorption as compared to 4the alpha-beta alloy C135AMO. It will further be noted `that the pickup tends to be greater in the stressed areas of these specimens than'in the nonstressed areas.

In order more clearly to compare the test results given in Tables IV and V for the alloys thereof, the results have been re-tabulated in the following Table VI for the various exposure times and for the non-stressed versus the stressed conditions to show the hydrogen pickup.

TABLE VI 30 DAYS A'I 400 o.-NoN-sTRnssED CONDITION Alloy Hai-1% O2 H2 Only H24- 0.1% H2O C135AMO 90 DAYS AT v400" C.NONSTRESSED CONDITION Additions in percent by volume.

TABLE VI-Continued 30 DAYS AT 400 o.-sTREssED CONDITION Alloy HTI-1% O2 Hg-l- H2 Only Referring to the foregoing data, it will be seen that for exposure times up to 90 days at 400 C., under the non-stressed condition, the RC900 alpha alloy is far superior to any of the others as regards hydrogen pickup, being substantially nil, although the alpha alloys ClZOAV and S-l-l show good performance up to 30 days exposure, especially in the oxygen-containing atmosphere. These three alloys also show excellent performance for exposures up to 30 days at 400 C. under stressed conditions n the oxygen-containing atmosphere. For an exposure time up to 90 days at 400 C. under the stressed conditions, the alloy RC900 shows the best performance in the oxygen-containing atmosphere while the 8-l1 alloy shows the best performance in `the water vapor-containing atmosphere.

The S10-day test at 400 C. is of course excessive and would never be encountered in operation, for example, of an electrical generator of the hydrogen-cooled type, nor in fact would 30 days of continuous operation at such temperature be encountered.

The invention is exemplified in one of its applications by the annexed drawing comprising a longitudinal sectional elevation of an alternating current generator mounted in a gas-tight housing filled with a hydrogencontaining atmosphere according to the invention, and wherein the armature retaining rings are made of an alpha titanium base alloy according to the invention.

Referring to the drawing, the stator is shown at 10 and the rotor or armature at 11. Mounted on the armature are armature retaining rings 1.2-4.3, made of an allalpha or substantially al1-alpha titanium base alloy according to the invention, these rings being preferably vacuum annealed and surface oxidized prior to installation for minimizing hydrogen pickup as explained above. The retaining rings are backed by support rings 14, 15, which may also be made of a titanium base alloy of the type aforesaid. The armature is mounted on a shaft 17, journaled at its opposite ends in bearing members i, 19, carried by supports 20, ffl. The armature sha- Pt carries the usual slip rings 22, for tapping o the alternating current power supply. The armature and stator assembly is mounted Within a housing 2,3, lled with an atmosphere 24 consisting of hydrogen and 0.1 to 1% of oxygen and/or Water vapor in accordance with the invention. This atmosphere is circulated by means of fan blades 25, 26, mounted on the rotor shaft, which circulate the hydrogen-containing atmosphere to and from a Water cooling unit 217 in the manner shown by the arrows, thus to cool the rotor and stator elements and appurtenant components.

As shown by the above test results, preferred alpha alloys for purposes of the invention are those containing zirconium, preferably together With aluminum and/ or tin. Excellent alloys ror such applications are the following: Ti-(3-6)% Al-(4-15)% Zr, Ti-(3l0)% Al-(4- Zr and Ti-(3-6)% Al-(4-10)% Sn-(5-10)% Zr. These alloys have excellent elevated temperature strength and creep resistance and also excellent room temperature strength and ductility. They are inherently relatively resistant to hydrogen pickup at elevated temperatures up to 400 C., particularly when vacuum annealed and therea'iiter air oxidized. Also they are not embrititled by hydrogen pickup.

What is claimed is:

1. An `article made of Va titanium base alloy containing about 5 to 30% of at least one alpha promoter selected from the group consisting of aluminum, tin and zinconium, up to about 5% of beta -isomorphous promoters of the group vanadium, molybdenum, columbium and tantalurn, balance substantially titanium, said article having `an oxidized surface `and being characterized by retention of high strength and ductility on prolonged exposure to hydrogen and hydrogen-containing atmospheres at temperatures up to about 400 C. and being resistant to hydrogen absorption tat such temperatures.

2. An article made of a titanium base alloy containing about 3 to 6% aluminum, 4 to 15% zirconium, up to 5% iof beta isomorphous promoters of the group vanadium, molybdenum, columbium and tantalum, balance substantially titanium, said article having an oxidized surface `and `being characterized by retention of high strength and ductility on prolonged exposure to hydrogen and hydrogen-containing atmospheres at temperatures up to about 400 C., and being resistant to hydrogen absorption at such temperatures.

3. An anticle made of a .titanium base alloy containing about 3 tto 6% aluminum, 4 to 10% tin, 5 to 10% zirconium, up to 5% of beta isornorphous promoters of the group vanadium, molybdenum, columbium and tantalum,

10 balance substantially titanium, said article having an oxidized surface and being characterized by retention of high strength vand ducti-lity on prolonged exposure to hydrogen `and hydrogen-containing atmospheres iat temperatures up to about 400 C., and being resistant to hydrogen absorption at such temperatures.

4. An article rnade of a titanium base alloy containing `about 3 to 10% of metal of the group aluminum and tin, but not to exceed about 6% aluminum, about 4 to 15% zirconum and the balance substantially titanium, said a-rticle having `an oxidized surface and being characterized by retention of high strength and rductility on prolonged exposure -to hydrogen and hydrogen-containing atmospheres at temperatures up to about 400 C., and being resist-ant to hydrogen absorption at such temperatures.

5. An article made of :a titanium base alloy containing Iabout 3 rto 6% aluminum, :about 4 to 15% zirconium, and the balance substantially titanium, said article having an oxidized surf-ace and being chanacterized by retention of high strength and ductility on prolonged exposure to hydrogen and hydrogen-containing atmospheres at temperatures up to about 400 C., and *being resistant to hydrogen absorption at such temperatures.

6. The method of minimizing hydrogen absorption in articles made of titanium and titanium base alloys eX- posed in service to hydrogen atmospheres at temperatures up -to 'about 400 C., which consists in maintaining in said hydrogen atmosphere about 0.1 to 1% by volume of at least one gas selected lfrom the group consisting of oxygen and water vapor.

7. ln combination: ian electrical current generator, a substantially gas-tight housing encasing the same, a lowdensity, heat-transferring atmosphere within said housing, consisting 'off hydrogen containing about 0.1 to 1% of at least one member of the group consisting of oxygen and Water vapor, land at least one component of said generator exposed to said `atmosphere Within said housing being composed of la metal of the group consisting of titanium and titanium base alloys.

8. ln combination: an electrical current generator, a substantially lgas-tight housing encasing the same, a lowdensity, heat-transferring atmosphere within said housing, consisting of hydrogen containing about 0.1 to 1% of at least one member of the `group consisting of oxygen and Water vapor, and at least one component of said generator exposed to said Iatmosphere Within said housing `being made of `a titanium base alloy containing about 5 to 30% of at least one alpha promoter selected from the group consisting of aluminum, tin yand zirconium, up lto about 5% of isomorphous beta promoters of the group vanadium, molybdenum, columbium and tantalum, balance substantially titanium.

References Cited in the le of this patent UNITED STATES PATENTS 2,394,110 Savage Feb. 5, 1946 2,669,513 y.aee Feb. 16, 1954 2,797,996 .Toffee July 2, 1957 2,392,742 ZWiCker .lune 30, 1959 2,393,864 Harris July 7, 1959 2,918,367 yCrossley Dec. 22, 1959 

8. IN COMBINATION: AN ELECTRICAL CURRENT GENERATOR, A SUBSTANTIALLY GAS-TIGHT HOUSIG ENCASING THE SAME, A LOWDENSITY, HEAT-TRANSFERRING ATMOSPHERE WITHIN SAID HOUSING, CONSISTING OF HYDROGEN CONTAINING ABOUT 0.1 TO 1% OF AT LEAST ONE MEMEBER OF THE GROUP CONSISTING OF OXYGEN AND WATER VAPOR, AND AT LEAST ONE COMPONENT OF SAID GENERATOR EXPOSED TO SAID ATMOSPHERE WITHIN SAID HOUSING BEING MADE OF TITANIUM BASE ALLOY CONTAINING ABOUT 5 TO 30% OF AT LEAST ONE ALPHA PROMOTER SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, TIN AND ZIRCONIUM, UP TO ABOUT 